1. Field of the Invention
This invention relates generally to maximizing the efficiency of radio frequency power amplification in a wireless communication device transmitter, and, more particularly, to a high efficiency multi-level power amplifier.
2. Related Art
With the increasing availability of efficient low cost electronic modules, mobile communication systems arc becoming more widespread. For example, there are many variations of communication schemes in which various frequencies, transmission schemes, modulation techniques and communication protocols are used to provide two-way voice and data communications in a hand-held telephone-like wireless communication handset. While the different modulation and transmission schemes each have advantages and disadvantages, one common factor is the need for highly efficient power amplification. As these communication devices become smaller, the benefits provided by highly efficient power amplifiers becomes increasingly important. One significant concern when developing these handheld communication devices is power consumption. A high efficiency power system decreases the amount of power consumed, thereby maximizing the power source life of the device.
Another concern in these wireless devices is the size of the circuitry. In order to minimize the size of the wireless communication device, it is desirable to integrate as much functionality as possible into fewer and fewer circuit modules. This enables the wireless communication device to be smaller. Integrating components also provides the benefit of less power consumption. Smaller wireless communication devices are more desirable by consumers in the marketplace.
Most power amplifier systems employed in wireless communication devices must operate efficiently over a broad range of operating power levels. Efficient operation is inherently difficult to achieve without complex circuitry and logic to control the power amplifier(s). Typically, additional circuitry residing on a control die must be used to control the power amplifier circuit. However, this additional circuitry requires additional space, thereby making the wireless communication device larger, and utilizes additional power. Also, this circuitry adds additional cost to each unit.
One conventional manner to achieve high efficiency power amplification over a broad range of power output levels uses radio frequency (RF) switches to select different power amplifiers based upon the required power output demand. Each of the power amplifiers is optimized for high efficiency at different power levels. Unfortunately, this technique requires the use of an additional control die to house the RF switches. The control die results in an additional cost per unit, increases the size of the wireless communication device, and also consumes additional power.
Another conventional manner to achieve high efficiency power amplification over a broad range of power output levels involves two separate amplifiers, each amplifier having different characteristics and each amplifier optimized for high efficiency at different power levels. In such an arrangement, the amplifiers could be activated separately with separate control dies to satisfy the required power levels. a hat is, only one of the two power amplifiers is on at any given time. Microwave couplers may be used to ensure the correct phase match between the two amplifiers. Unfortunately, this technique still requires a separate control die. Furthermore, the two different amplifiers must have a matched phase supplied at their input, thereby requiring that the microwave couplers be extremely stable.
Therefore, there is a continuing effort in the industry to develop a wireless power amplification circuit that achieves highly efficient power amplification over a broad range of output power levels and that is economical to mass produce in high volume.
The invention provides a high efficiency multi-level power amplifier that maximizes power amplifier efficiency and minimizes the required control circuitry. Thus, the invention increases the power efficiency of a power amplifier circuit by integrating many of the power amplifier components and control circuitry onto an integrated circuit (IC). Also, the integration of all components onto a single IC simultaneously minimizes the amount of control circuitry required to control the amplifier, thereby allowing a reduction in size of the wireless device. Furthermore, the single IC may reduce the manufacturing cost of each wireless device.
The high efficiency multi-level power amplifier utilizes two amplifiers having different amplification characteristics that are connected to two RF couplers. The power amplifier circuit uses both amplifiers when power demand is high and uses the output of a single power amplifier when power demand is lower. By utilizing power amplifiers having different amplification characteristics, the output of the wireless device when operating in the low power operating condition is set to an optimized level for a low power operation mode and is set to another optimized level for a high power operation mode.
In another embodiment, the multi-level power amplifier is configured such that the isolated port of each RF coupler is connected to an impedance modification circuit. When using only one power amplifier, the impedance modification circuit eliminates the impedance mismatch caused by the single power amplifier operation by using an externally biased semiconductor to present the proper impedance to the coupler connected to the inactive power amplifier. In this manner, any impedance mismatch between the operative and inoperative power amplifiers is compensated, thus allowing the single operating power amplifier to achieve optimal performance. Related practices of operation and computer readable media are also provided.
Other systems, methods, features and advantages of the invention will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.